1. FIELD OF THE INVENTION
The present invention relates to laminated damping materials for vehicles and particularly to those which are in use welded onto vehicle body panels such as floor panels, and further to a method for welding such materials to the panels.
2. DESCRIPTION OF THE PRIOR ART
A vehicle such as an automobile is generally constructed to have a floor panel as part of its body bonded with a damping material thereon in order to improve vibration proofing, thermal insulation and sound insulation properties of the panel.
There are conventionally known as such a damping material one which is formed of a single mer-sheet including asphalt as a primary constituent and is thermally welded onto a floor panel, or one comprising, as shown in Japanese Patent Application Laid-open No. 63542/83, a sub panel which is fixed by clips to a floor panel through a mer-sheet interposed therebetween, the mer-sheet serving to provide a thermal welding between the floor and sub panels.
A floor panel in an automobile body structure, however, is generally constructed by using a steel plate having a thickness less than 1mm so that to compensate for the rigidity of such thin steel plate its surface is bent or beads are provided thereon so as to have an irregular or rugged cross-sectional shape.
In case of the afore-mentioned conventional damping material having a mer-sheet merely welded onto the floor panel, irregularities of the floor panel appear on the upper surface of the damping material and even when a mat is laid on the material, passengers in a vehicle compartment may still feel the irregularities of floor surface, thus deteriorating an impression given to the passengers.
When a mer-sheet and a sub panel are superposed together and are thermally welded as a damping material onto a vehicle floor panel as shown in Japanese publication No. 63542/83, it is required to bend the sub panel itself so as to conform to the configuration of the mating floor panel surface in order to obtain an intimate contact between the damping material and the rugged floor surface. This makes laminated damping materials expensive in the market and also makes it troublesome to fit the ruggedness on a sub panel to the ruggedness on a floor panel surface in assembly line.